Soil Organic Matter and Amorphous Oxides Determine the Surface Electrochemical Properties of Purple Soil Under Long-Term Inorganic and Organic Fertilization

Soil surface electrochemistry is a science that studies the interaction and chemical behavior of charged particles (colloidal particles, ions, protons and electrons) in soil. Surface electrochemical properties (SEP) of soil have significant influences on soil fertility, aggregate stability, and contaminant migration. However, the impacts of long-term fertilization on SEP of purple soil (Eutric Regosol, FAO soil classification) have received little attention, and the factors affecting SEP also remain unclear. This study examined the effects of long-term fertilization on SEP. A field fertilization trial was established in 1991 with four treatments: no fertilization (CK), chemical fertilizer (NPK), chemical fertilizer plus pig manure (NPKM), and chemical fertilizer plus rice straw (NPKS). Soil SEP (surface potential, φ₀; surface charge density, σ₀; surface electric field strength, E; specific surface area, SSA; surface charges number, SCN) and mineralogy properties was determined. Compared with CK, NPK, NPKM, and NPKS significantly increased φ₀ by 5.21% to 20.4%, and SSA by 16.5% to 31.6% (P < 0.05). NPKM and NPKS increased σ₀ by 8.69% to 17.4%, E by 9.48% to 15.9%, and SCN by 5.21% to 20.4% (P < 0.05). In addition, NPKM and NPKS increases soil organic matter (SOM) and amorphous oxides. Redundancy analysis indicated that SOM, amorphous manganese oxides (Mno), amorphous aluminum oxides (Alo) and amorphous iron oxides (Feo) could explain 80.6%, 5.2%, 3.9% and 2.7% of the variation in SEP, respectively. Therefore, long-term inorganic and organic fertilization primarily affected purple soil SEP by regulating SOM and amorphous oxides (Mno, Alo, and Feo). The increasing of SOM content it is the key point to improving soil quality.